Brake boost sensor feeler

ABSTRACT

The invention relates to a sensor feeler device for a brake booster. In this device, the sensor feeler device ( 4 ) comprises:
         an axially moveable cylinder ( 40 ) the movement of which can be controlled by the control rod which is itself controlled by the brake pedal,   a sensor feeler piston ( 5 ) able to move axially in said moving cylinder ( 40 ),   a spring ( 44 ) that tends to push the sensor feeler piston ( 5 ) forward and keep its front face substantially in the same plane as the front face of the moving cylinder.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a brake booster with a variable boost ratio.The invention is more particularly applicable to brake boosters formotor vehicles.

A brake booster like the one depicted in FIG. 1 essentially comprises,in a sealed casing 10, two chambers (the front chamber 10 av and therear chamber 10 ar) which are separated by a moving membrane 14.

A control rod 20 can move towards the front of the vehicle (in thedirection of arrow F1 in FIG. 1) when the driver of the vehicledepresses the brake pedal. This movement of the control rod 20 istransmitted to a slide valve plunger 21 which actuates boost means. Asis known in the art, these boost means generally comprise a three-wayvalve, actuation of which makes it possible either to place the frontchamber 10 av of the booster in communication with the rear chamber 10ar, or to interrupt this communication, or to place the rear chamber incommunication with the surrounding atmosphere.

The front chamber 10 av is normally under vacuum. At rest (when there isno brake command), the two, front and rear, chambers are incommunication with one another and the same pressure is obtained in eachof the two chambers.

When the driver depresses the brake pedal, the control rod 20 is movedforward (to the left in the figure). The slide valve plunger 21 is movedforward and causes the three-way valve to operate. This valve isolatesthe two, front and rear, chambers and places the rear chamber incommunication with atmospheric pressure.

Because of the difference in pressure between the two chambers, a boostforce is applied to the moving membrane 14 separating the two chambers.This moving membrane 14 is associated with a skirt 15 made of a rigidmaterial. Under the effect of the boost force, the moving membrane tendsto move forward and carries the skirt 15 along with it.

The skirt 15 itself carries along the piston 22 which therefore movesforward (in the direction of the arrow F1), acting on a push rod 30which serves to actuate a piston of the master cylinder 61 of thebraking circuit.

In the conventional way, in a booster design such as this, the slidevalve plunger 21 slides in a bore of the hub of the piston 22 and formsa thrust member acting on a reaction disk 23 which transmits force tothe push rod 30.

This reaction disk 23 rests against the front face of the plunger andagainst the front face of the piston surrounding the plunger.

In a system such as this, the brake booster has a fixed boost ratio.However, under certain operating circumstances, for example in the eventof emergency braking, it may be advantageous to provide a boost force asearly as possible.

This is why, in some systems, there is, between the control rod 20 andthe reaction disk 23, a sensor feeler which slides in a cylinder able tomove axially inside the piston. FIGS. 2 a and 2 b depict a system suchas this which is described, for example, in Patent EP 1 322 510.

In this system, there is therefore a sensor feeler 31 able to moveaxially inside a cylinder 34 which is able to move axially inside thepiston 22. The spring 32 tends to push the cylinder 34 to the left andto bring the end 35 of the sensor feeler 31 closer to the left-hand endof the cylinder 34. In that system, the force of the control rod 20 isexerted via the slide valve plunger 21 on the sensor feeler 31.

The invention relates to an improvement to this type of device that hasthe advantage of being easier to manufacture and of reducing the timetaken to assemble the booster.

The invention therefore relates to a sensor feeler device for a brakebooster, comprising:

a pneumatic control device controlled by a three-way valve,

a slide valve plunger providing control of the pneumatic control device,

a control rod intended to apply an axial movement force to the slidevalve plunger,

a piston able to move axially under the control of the pneumatic controldevice,

a push rod receiving axial movement forces from said moving piston andfrom the slide valve plunger and forwarding them to a brake mastercylinder,

a reaction disk positioned between the control rod and the push rod,

a sensor feeler device able to move axially and situated between thereaction disk and the control rod.

According to the invention, the sensor feeler device comprises:

an axially moveable cylinder the movement of which can be controlled bythe control rod,

a sensor feeler piston able to move axially in said moving cylinder,

a spring that tends to push the sensor feeler piston forward and keepits front face substantially in the same plane as the front face of themoving cylinder.

According to one advantageous embodiment of the invention, the movingcylinder comprises a cavity capable of accepting, such that it can slideaxially, the moving sensor feeler piston. The moving cylinder comprisesa shoulder that forms a stop for a thrust piece of the sensor feelerpiston and limits the forward movement of the sensor feeler piston.

In addition, the moving cylinder advantageously comprises a rear part.Said spring rests, on the one hand, against this rear part and, on theother hand, against the sensor feeler piston.

According to one embodiment, said rear part is welded to the movingcylinder.

According to another form of embodiment, the said rear part and themoving cylinder are made as one piece.

Provision may also be made for the side wall of the moving cylinder tocomprise an aperture to allow the thrust piece of the sensor feelerpiston to slide.

Advantageously, provision will also be made for the rear part tocomprise a first axial boss for centering the spring.

According to an alternative form of embodiment, the sensor feeler pistonhas a second axial boss also for centering the spring.

To allow the plunger piston to be fitted into the moving cylinder, theaxial length of the aperture and the distance separating the front faceof the first boss from the shoulder of the moving cylinder are bothgreater than the total axial length of the plunger piston. In thisembodiment, in which the plunger piston and the thrust piece are made intwo parts, provision may be made for this distance simply to be greaterthan the thickness of the thrust piece of the plunger piston.

In this form of embodiment, said aperture is wide enough to allow thethrust piece of the plunger piston through.

According to an alternative form of embodiment of the invention, theheight of the aperture is greater than the total axial length of theplunger piston, of its thrust piece and of its boss.

Provision may also be made for the plunger piston and its shoulder to bemade in two parts.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects and features of the invention will become moreclearly apparent in the following description and in the attacheddrawings which depict:

FIG. 1: a brake booster of the known art to which the invention applies;

FIGS. 2 a and 2 b: a device, known from the art, for transmitting forcesbetween the control rod driven by the brake pedal, on the one hand, andthe reaction disk, on the other;

FIGS. 3 a and 3 b: a device for transmitting forces, according to theinvention, between the control rod driven by the brake pedal, on the onehand, and the reaction disk, on the other;

FIGS. 4 a and 4 b: an alternative form of embodiment of the device ofFIGS. 3 a and 3 b.

DETAILED DESCRIPTION

With reference to FIGS. 3 a and 3 b, there will first of all bedescribed one exemplary embodiment according to the invention of adevice for transmitting forces between the piston of the booster and theslide valve plunger driven by the control rod on the one hand and thereaction disk associated with the push rod controlling the pistons ofthe master cylinder, on the other.

This device applies to a brake booster like that of FIG. 1. These FIGS.3 a and 3 b depict only that part of the booster that contains thedevice of the invention. The components depicted in FIGS. 3 a and 3 bbear the same references as those components of FIGS. 1, 2 a, 2 b thatperform the same functions.

By convention, in this description, the terms “front” and “rear” relaterespectively to “left” and “right” in the attached figures.

These figures then show the control rod 20 which controls the movementof the slide valve plunger 21 which initiates operation of the brakebooster and causes its piston 22 to move under the effect of thedifference in pressure between the front and rear chambers of thebooster. They also show the reaction device (reaction disk) 23 and thepush rod 30 which forward the forces to the pistons of the mastercylinder, and vice versa.

The slide valve plunger 21 presses against the reaction disk via asensor feeler 4.

This sensor feeler comprises a cylinder 40 able to move axially in abore belonging to the piston 22. The moving cylinder 40 contains anaxially moveable sensor feeler piston 5.

The sensor feeler piston 5 comprises a moving piston 50 and a thrustpiece 51 the forward movement of which is restricted by a shoulder 42belonging to the moving cylinder.

A spring 44 rests against a wall 45 of the rear part 41 of the movingcylinder and tends to keep the sensor feeler over toward the left bypressing against the thrust piece 51.

A central boss 47 centers the spring 44 in the moving cylinder.

According to this design of sensor feeler 4, the thrust force exerted bythe slide valve plunger 21 to the push rod 30, is transmitted mainly bythe moving cylinder 40. The reaction from the master cylinder will beapplied to the moving piston 50 of the sensor feeler via the reactiondisk.

The system of the invention differs from the prior art in which thethrust force from the control rod is exerted by the moving sensor feeler(31 in FIGS. 2 a and 2 b).

In this design, the sensor feeler 4 may then be made as a one-pieceentity.

According to a first embodiment, the rear part 41 may be welded orbonded, at points 48 and 49, to the body of the moving cylinder once themoving piston 50 and the thrust piece 51 have been fitted into the bore43 of the moving cylinder.

According to a second embodiment, the body of the moving cylinder andthe rear part 41 are made as a single piece. The moving piston 50 andthe thrust piece 51 are mounted inside the bore 43 by inserting themthrough the opening 46 made in the wall of the moving cylinder.

In order for that to be possible, the dimension L1 of the opening andthe distance L4 separating the boss 47 from the shoulder 42 need both tobe greater than the axial length L5.1 of the piston 50 of the sensorfeeler and of the thrust piece 51.

FIGS. 4 a and 4 b depict an alternative form of embodiment of theplunger 5 according to the invention.

In this alternative form, the piston of the plunger and the thrust pieceare made as a single piece 52. The plunger piston therefore has ashoulder 53 which limits its forward movement. In addition, in FIGS. 4 aand 4 b, it is the piston 52 of the plunger that has a boss 54, ratherthan the wall 45 of the rear part 41 of the moving cylinder 4, forcentering the spring 44.

As in the embodiment of FIGS. 3 a and 3 b, the rear part 41 is welded orbonded to the body of the moving cylinder.

When the rear part 41 and the body of the moving cylinder are made as asingle piece, the dimension L2 of the aperture 46 needs to be greaterthan the axial dimension L5.2 of the plunger 5 so as to allow it to bemounted in the moving cylinder 4.

1. Brake booster with a variable boost ratio comprising: a pneumaticcontrol device (10, 14, 15) controlled by a three-way valve, a slidevalve plunger (21) providing control of the pneumatic control device, acontrol rod (20) intended to apply an axial movement force to the slidevalve plunger, a piston (22) able to move axially under the control ofthe pneumatic control device, a push rod (30) receiving axial movementforces from said moving piston and from the slide valve plunger (21) andforwarding the forces to a brake master cylinder, a reaction disk (23)positioned between the control rod (21) and the push rod (30), and asensor feeler device (4) able to move axially and situated between thereaction disk (23) and the control rod (20), the sensor feeler device(4) comprising: an axially moveable cylinder (40) the movement of whichcan be controlled by the control rod, a rear part (41) welded or bondedto the axially moveable cylinder (40) to form a single piece, a sensorfeeler piston (5) able to move axially in said moving cylinder (40), aspring (44) that tends to push the sensor feeler piston (5) forward andkeep its front face substantially in the same plane as the front face ofthe moving cylinder.
 2. Sensor feeler device according to claim 1,characterized in that the moving cylinder (40) comprises a cavity (43)capable of accepting, such that it can slide axially, the moving sensorfeeler piston (5), the moving cylinder (40) comprising a shoulder (42)that forms a stop for a thrust piece (51) of the sensor feeler piston(5) and limits the forward movement of the sensor feeler piston. 3.Sensor feeler device according to claim 2, characterized in that themoving cylinder (4) comprises a rear part (41), the spring (44) resting,on the one hand, against this rear part and, on the other hand, againstthe sensor feeler piston (5).
 4. Sensor feeler device according to claim3, characterized in that said rear part (41) is welded or bonded to themoving cylinder (40).
 5. Sensor feeler device according to claim 3,characterized in that the said rear part (41) and the moving cylinder(40) are made as one piece.
 6. Sensor feeler device according to claim1, characterized in that the side wall of the moving cylinder (40)comprises an aperture (46) to allow the thrust piece (51) of the sensorfeeler piston (5) to slide.
 7. Sensor feeler device according to claim3, characterized in that the rear part (41) comprises a first axial boss(47) for centering the spring (44).
 8. Sensor feeler device according toclaim 3, characterized in that the sensor feeler piston (5) has a secondaxial boss (54) for centering the spring (44).
 9. Sensor feeler deviceaccording to claim 7, characterized in that the axial length (L1) of theaperture (46) and the distance (L4) separating the front face of thefirst boss (47) from the shoulder (42) of the moving cylinder (40) areboth greater than the total axial length (L5.1) of the plunger piston(5).
 10. Sensor feeler device according to claim 3, characterized inthat the plunger piston (50) and the thrust piece (51) are made in twoparts.
 11. Sensor feeler device according to claim 10, characterized inthat the axial length (L1) of the aperture (46) and the distance (L4)separating the front face of the first boss (47) from the shoulder (42)of the moving cylinder are both greater than the thickness of the thrustpiece (51) of the plunger piston (5).
 12. Sensor feeler device accordingto claim 9, characterized in that said aperture (46) is wide enough toallow the thrust piece (51) of the plunger piston (5) through. 13.Sensor feeler device according to claim 8, characterized in that theaxial length (L2) of the aperture (46) is greater than the total axiallength of the plunger piston (52), of its shoulder (53) and of its boss(54).